Conventional basestation transmitters typically have a plurality of radio channel units each assigned to dedicated amplifier resources and dedicated antennas. There may be an individual amplifier for each radio channel unit, or several of the radio units may have their signals combined before being amplified. These are inefficient and inflexible ways to allocate amplifier resources. To illustrate the limitations of such current systems, consider a tri-sectored system having sectors X, Y, Z with 10 available physical user assigned radio channel units per sector, and for simplicity assume a radio channel unit can service only one caller at a time. Then in the situation when there is an uneven loading of say 6, 9, and 12 users in sectors X,Y and Z respectively, then callers 11 and 12 in sector Z will be blocked. This blocking is done by virtue of there not being enough radio channel units assigned to sector Z, even though there are 5 unassigned radio channel units in the remaining sectors.
European patent application no. EP 704964 made public on Apr. 3, 1996 to Meredith, entitled "Power Sharing System for High Power RF Amplifiers" discloses a system for amplifying a plurality N of antenna inputs in which the amplification load of all the antenna inputs is spread evenly across a plurality N of amplifiers and more importantly in which radio channel units are assignable to any antenna. An input transform matrix divides each signal to be amplified into N divided signals, each divided signal having a fraction 1/N of the power of the original signal. The input to each amplifier is a combination of a divided signal from each signal to be amplified. Each amplifier produces an amplified combination of the divided signals. An output transform matrix then recombines the divided signals so as to produce amplified versions of the signals to be amplified. Meredith points out that it is important that the phase shift introduced in each of the input transform matrix, the amplifiers and the output transform matrix must be balanced such that the recombined signals do not contain undesired components from incorrect input signals. It is suggested that such phase balancing may be accomplished by controlling the lengths of certain signal lines, and/or by adjusting the phase shift introduced by the amplifiers.
Meredith does not suggest how to control the lengths of the signal lines or how the phase shift adjustments for the amplifiers is achieved. Furthermore, Meredith does not mention that in addition to phase balancing, gain balancing must also be performed. If any type of gain or phase mismatch is introduced, then the output signals will contain undesirable components.